> \LCY-cmd contains an explicit warning \@inmathwarn.

Inputenc currently enforces all characters to be declared as text or
math, but not both. (Allowing use of both in general is very expensive
as normally in text mode it uses \chardef, but \chardef'ed tokens
don't work in math mode, so it would require twice as many csnames, so
that some math-mode version could be declared as well (cf
\textsterling and \mathsterling, and \pounds which uses one or the other)
However it may be possible to do something in this case.